Optical fiber connectors are an essential part of substantially all optical fiber communication systems. For instance, such connectors are used to join segments of fiber into longer lengths, to connect fiber to active devices such as radiation sources, detectors and repeaters, and to connect fiber to passive devices such as switches and attenuators. The principal function of optical fiber connectors is to hold an optical fiber such that its core is axially aligned with the optical path of the device to which the connector is mating (e.g., another fiber). This way, the light from one fiber is optically coupled to the optical path of the mating device.
Often there is a need to define the optical fiber's radial position with respect to the connector. Such a need arises, for example, with the use of polarization maintaining (PN) optical fibers. To connect polarization-maintaining optical fibers or to connect a polarization-maintaining optical fiber and another device, the polarization planes of the fibers need to coincide with each other with a high degree of accuracy. For this reason, the connection relies on the individual radial adjustment of each fiber.
Another instance in which it is desirable to set the radial position of the fiber relative to the connector is in the use of single mode fibers. More specifically, it is common in single mode applications to use fibers which have beveled end faces. The beveled end face is usually about 7° off perpendicular from the optical transmission path of the fiber, and insures that any light which is reflected from the end face interface is not reflected back down the optical transmission path. This way, damage to the light generating source (e.g. laser) is avoided. Since the end faces of mating single mode fibers are beveled, if they are not radially aligned with one another, their bevels will not be complementing, but rather interfering such that a gap between the end faces results when the fibers are mated. Therefore, to ensure that the beveled end faces mate in a complementary fashion, it is essential that each fiber be held in the mating connectors in a particular radial position.
Yet another instance in which a fiber's radial position with respect to the connector is critical is in minimizing the insertion loss of a connector. More specifically, due to the asymmetry typically found in ferrules (e.g., non-axial alignment of the fiber and apex offset), light transmission between mating ferrules is a function of the radial orientation between the two mating ferrules. Therefore, it is desirable to establish the radial position of the fiber relative to the housing of the connector such that insertion losses are minimized.
Traditional approaches for effecting the relative radial position of the optical fiber to the connector tend to be either complicated or too coarse to realize the precise radial positioning often required. For example, a popular approach for radially positioning the fiber in a LC type connector involves securing the fiber to the ferrule and then moving the ferrule assembly in quarter rotation increments until the lowest insertion loss of the four different positions is determined. Although this approach provides for some tuning of the connector, the applicants recognize that often times four predetermined radial positions are not adequate to realize the low insertion loss potential of the connector.
Another approach for establishing the radial position of the optical fiber relative to the connector is described in U.S. Pat. No. 5,668,905 (herein referred to as the 905 patent). The 905 patent is directed to establishing the radial position of a polarization maintaining fiber in an optical connector. It involves sliding an angular index member over the ferrule assembly and then, while viewing the fiber under a microscope, rotating the ferrule assembly until the desired alignment with respect to the microscope is achieved. At this point, adhesive is applied to the interface of the angular index member and the ferrule assembly such that the angular index member becomes fixed to the ferrule assembly. This assembly then is incorporated into an optical connector in which the radial position of the angular index member and the housing of the connector is predetermined. Although this approach is effective in establishing a high degree of “tuning” with respect to the radial position of the fiber to the housing, its use of adhesive tends to complicate its implementation and limit the conditions under which this radial alignment approach can be undertaken.
Additionally, applicants note that the angular index member used in the 905 patent will tend to introduce a certain amount of play between the ferrule assembly and the housing. More specifically, since the radial positioning means on the annular index member (i.e., the key ways) have very little radial offset from the center of the ferrule assembly, any tolerance in the key way will tend to have a significant impact on the radial orientation of the ferrule assembly.
Therefore, there is a need for establishing the radial position of the fiber relative to the connector which is simple and effective. The present invention fulfills this need among others.